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J. Biol. Chem., Vol. 279, Issue 13, 12076-12080, March 26, 2004

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Activation of Glycogen Phosphorylase with 5-Aminoimidazole-4-Carboxamide Riboside (AICAR)

ASSESSMENT OF GLYCOGEN AS A PRECURSOR OF MANNOSYL RESIDUES IN GLYCOCONJUGATES^*

Jie Shang and Mark A. Lehrman

From the Department of Pharmacology, University of Texas Southwestern Medical Center, Dallas, Texas 75390-9041

The experimental evaluation of the contribution of glycogen phosphorylase (GP) to biochemical pathways is limited to methods that raise cAMP, activating the cAMP-dependent protein kinase/phosphorylase kinase/GP cascade. Such methods convert the unphosphorylated form, "GPb," which catalyzes glycogenolysis only in the presence of appropriate allosteric activators such as AMP, to the phosphorylated, constitutively activated form, "GPa." However, activation of GP in this way is indirect, requires a functional cAMP kinase cascade, and is complicated by other actions of cAMP. Here, we demonstrate a strategy for the experimental manipulation of GP in intact dermal fibroblasts, involving activation by the membrane-permeable adenosine analog 5-aminoimidazole-4-carboxamide riboside (AICAR) and inhibition by caffeine and Pfizer compound CP-91149, which bind to GP at distinct sites. Potential complications because of activation of AMP-activated protein kinase by AICAR were assessed with metformin, which activates this kinase but does not activate GP. Using this strategy, we show that glycogen can be a significant and regulatable precursor of mannosyl units in lipid-linked oligosaccharides and glycoproteins.

Received for publication, January 14, 2004

^* This work was supported by Grant GM38545 from the National Institutes of Health and Grant I-1168 from the Robert Welch Foundation. The costs of publication of this article were defrayed in part by the payment of page charges. This article must therefore be hereby marked "advertisement" in accordance with 18 U.S.C. Section 1734 solely to indicate this fact.

To whom correspondence should be addressed. Tel.: 214-648-2323; Fax: 214-648-8626; E-mail: mark.lehrman{at}utsouthwestern.edu.

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